Method for hardening the wear portion of a retaining ring

ABSTRACT

A one piece plastic or two piece, metal and plastic, retaining ring used for chemical mechanical polishing of semiconductor substrates. In one embodiment, the plastic is selected from polyphenylene sulfide (PPS), polyethylene terephthalate, polyetheretherketone, polybutylene terephthalate, Ertalyte TX, PEEK, Torlon, Delrin, PET, Vespel, or Duratrol. The plastic wear surface is hardened by electron beam or gamma ray irradiation.

RELATED APPLICATIONS

This application is related to and claims priority from U.S. Provisional patent application No. 60/485,572 filed Jul. 8, 2003.

FIELD OF INVENTION

This invention relates to an electron beam radiation and gamma ray radiation process for hardening the wear portion of a one part or two part retaining ring typically used in chemical mechanical polishing operations.

BACKGROUND

The present invention relates to a retaining ring used in the process of chemical mechanical polishing of semiconductor substrates. The substrate is typically a thin disc of semiconductor material with deposited alternate layers of conductive, semiconductive, and insulating materials. The layers are etched to produce electrical circuitry on the surface of the substrate. A typical substrate has a series of layers deposited and circuitry etched. The deposition and etching process after many layers produces a non flat top surface. This lack of flatness prevents accurate deposition of subsequent layers. Planarization of the substrate is periodically required to maintain an acceptable substrate surface.

Chemical mechanical polishing of the topmost surface of the substrate produces a sufficiently flat surface to allow accurate subsequent deposition and etching of layers. This method of planarization is affected on a substrate by use of a polishing machine. Among the many subassemblies of this machine is the polishing head or carrier head. The polishing head contains among its components a retaining ring. This ring positions and retains the substrate allowing the other components of the head to exert pressure against the substrate which in turn moves relative to a polishing pad, usually wetted by a polishing medium or slurry.

In one embodiment, the retaining ring is formed from two pieces. The first, or upper, piece is usually of a metal material such as stainless steel, aluminum, or molybdenum, but may be other materials. The second, or lower, piece is of a plastic material such as polyphenylene sulfide (PPS), polyethylene terephthalate, polyetheretherketone, polybutylene terephthalate, Ertalyte TX, PEEK, Torlon, Delrin, PET, Vespel, or Duratrol.

In other embodiments, a single part plastic retaining ring may be provided.

There is a need for CMP retaining rings with harder surfaces which resist wear, thereby extending the life of the retaining ring.

SUMMARY

The invention is directed toward a method of treating the plastic wear portion of a retaining ring used in the chemical mechanical polishing process of a semiconductor substrate. The plastic portion of a one or two part retaining ring includes a wear surface which contacts a polishing pad. In one embodiment of the current invention, the lower wear surface of the plastic portion of the retaining ring is subjected to electron beam radiation in order to harden the surface. In another embodiment the wear surface is subjected to gamma ray radiation to harden the material.

The prior art establishes some improvement is material properties from electron beam radiation or gamma ray radiation of polymers. It is believed that such radiation has a detrimental effect because of the scission of polymer chains, but that this detrimental effect is partially offset at relatively low doses of radiation by the realignment of the rings which improves the surface hardness. It is desirable in semiconductor processing such as chemical mechanical polishing operations to provide a multi-layer ring that has a polymer wear portion which has improved wear characteristics. The wear characteristic is related to the hardness of the plastic, and radiation of a ring can improve the hardness and thereby improve wear characteristics of the retaining ring.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention are set forth below and further made clear by reference to the drawings, wherein:

FIG. 1 is a cross sectional view of the retaining ring.

FIG. 2 is a flow chart of a manufacturing process for a two part ring.

FIG. 3 is a flow chart of a manufacturing process for a one part ring.

DETAILED DESCRIPTION OF EMBODIMENT

Retaining Ring

Referring now to FIG. 1 which is a cross sectional view of a two part retaining ring, the retaining ring 10 is composed of an upper part 15 is typically made of a metal, and the lower part 25 is typically made of plastic. In one embodiment, the upper and lower parts are attached with an adhesive 50 such as an acrylic adhesive or a urethane adhesive. The lower part of the ring includes a wear surface 40.

Referring now to FIG. 2, in this embodiment the two part ring is fabricated by machining the metal upper portion at step 100, machining the lower plastic portion at step 110, joining the metal and plastic portion at step 120, processing the assembled ring at step 130, and hardening the plastic at step 140. The attachment at step 120 may be by adhesive attachment at step 122, or by mechanical attachment at step 125. Adhesive attachment typically includes grit blasting the mating surfaces of the metal and plastic parts with #24 ceramic abrasive to a finish of 150-250 RMS; degreasing the upper and lower portions, solvent cleaning the mating surfaces with acetone, applying an adhesive to the mating surface of the plastic portion of the ring, placing the metal portion on top of the plastic portion pressing the pieces together with a force of about 50 pounds until excess adhesive is squeezed out in a continuous bead around the ring and the adhesive has a thickness in the range of 0.007″ to 0.012″; removing the excess adhesive, and permitting the ring to cure at room temperature for a minimum of 24 hours. Adhesives, such as urethanes, acrylics, or epoxies may be used. In alternate embodiments, the two parts may be mechanically attached such as screwed together at step 124, or self threaded at step 128, or press fit at step 126.

In one embodiment, the first material is stainless steel and the second material is polyphenylene sulfide which includes TechTron^(R) by Quadrant, Ryton^(R) by Chevron-Phillips, and Ensinger by Ensinger Corporation.

Other plastics such as polyphenylene sulfide (PPS), polyethylene terephthalate, polyetheretherketone, polybutylene terephthalate, Ertalyte TX, PEEK, Torlon, Delrin, PET, Vespel, or Duratrol.

DETAILED DESCRIPTION OF EMBODIMENT

Electron Beam Radiation of Polyphenylene Sulfide Multilayer Ring

In this embodiment a multi-layer polyphenylene sulfide and metal ring is provided. After fabrication of the two part multi-layer ring at step 142, the PPS surface is subjected to electron beam radiation to harden the first few millimeters of depth. The electron beam irradiation is preferably between 0.5 and 2 MV. At a temperature of about 150□C. A temperature range of room temperature to slightly below the melting point of the plastic may be used.

In an alternative embodiment, the plastic portion of the ring may be treated by electron beam radiation before being assembled to the metal portion.

DETAILED DESCRIPTION OF EMBODIMENT

Electron Beam Radiation of Polyphenylene Sulfide Single Part Ring

Referring now to FIG. 3, in this embodiment a single part polyphenylene sulfide plastic retaining ring is fabricated at step 150. After fabrication, the PPS bottom wear surface is subjected to electron beam radiation at step 162 to harden the first few millimeters of depth.

DETAILED DESCRIPTION OF EMBODIMENT

Electron Beam Radiation of Other Plastic Rings

In this embodiment, a retaining ring is fabricated as a single part plastic ring or as a multilayer ring of metal and a plastic. The plastic may include polyphenylene sulfide (PPS), polyethylene terephthalate, polyetheretherketone, polybutylene terephthalate, Ertalyte TX, PEEK, Torlon, Delrin, PET, Vespel, or Duratrol.

DETAILED DESCRIPTION OF EMBODIMENT

Gamma Ray Radiation of Polyphenylene Sulfide

In this embodiment a multi-layer ring of polyphenylene sulfide and metal and is subjected to gamma ray radiation at step 144 after fabrication.

In an alternative embodiment, the plastic portion of the ring may be treated by gamma ray radiation before being assembled to the metal portion. The gamma ray radiation is preferably at a dose rate of 1 kGy/s by ⁶⁰Cobalt in a vacuum at a temperature of about 150□C. A temperature range of room temperature to slightly below the melting point of the plastic may be used.

DETAILED DESCRIPTION OF EMBODIMENT

In this embodiment the polyphenylene sulfide is a single part ring subject to gamma ray radiation at step 164 after fabrication of the ring. 

1. A method of fabricating a multilayer retaining ring for a CMP carrier head the method comprising machining a metal upper portion; machining a lower plastic portion; attaching the lower portion to the upper portion, such that the plastic portion has an exposed bottom surface; and treating the exposed plastic bottom surface with electron beam irradiation, thereby hardening the surface of the plastic portion.
 2. The method of claim 1 wherein the plastic is selected from the group from a material selected from the group consisting of polyphenylene sulfide (PPS), polyethylene terephthalate, polyetheretherketone, polybutylene terephthalate, Ertalyte TX, PEEK, Torlon, Delrin, PET, Vespel, or Duratrol;
 3. A method of fabricating a multilayer retaining ring for a CMP carrier head the method comprising machining a metal upper portion; machining a lower plastic portion; attaching the lower portion to the upper portion, such that the plastic portion has an exposed bottom surface; and treating the exposed plate surface with gamma ray irradiation, thereby hardening at least the surface of the plastic portion.
 4. The method of claim 1 wherein the plastic portion is selected from the group consisting of polyphenylene sulfide (PPS), polyethylene terephthalate, polyetheretherketone, polybutylene terephthalate, Ertalyte TX, PEEK, Torlon, Delrin, PET, Vespel, or Duratrol.
 5. A method of fabricating a plastic retaining ring, the method comprising machining the plastic ring, the ring having a lower wear surface; and hardening at least the wear surface of the ring with a radiation process.
 6. The method of claim 5 wherein the radiation process is an electron beam process.
 7. The method of claim 5 wherein the radiation process is a gamma ray process. 